Plasma etching has become the preferred technique for etching patterns in the various layers utilized in the manufacture of integrated circuit devices. The apparatus for such etching typically includes a chamber housing a pair of essentially planar electrodes that are spaced apart in a parallel relationship to define an interaction space therebetween. On a first of the electrodes is positioned a semiconductive wafer being processed. For such processing, an appropriate gaseous medium is introduced into the chamber and then one or more suitable high radio-frequency voltages are impressed across the pair of electrodes to generate a discharge and form a plasma that etches suitably exposed regions of the wafer.
It has become of increasing importance both for efficiency and for uniformity to confine the plasma essentially to the interaction space between the two electrodes. To this end, it has been proposed to include a ring-shaped element (a confining element or member) of a dielectric material at the periphery of one or both of the electrodes to confine the discharge to the interaction space (e.g., see U.S. Pat. No. 5,413,675 that issued on May 9, 1995). Alternatively, it has been known to include a cylindrical anodized aluminum shield to enclose the interaction space between the two electrodes with holes being provided in the shield to permit egress of the spent gases from the enclosed interaction space. This conductive shield is typically electrically connected to one of the electrodes which is connected to ground potential. This shield serves to effectively bring ground potential close to the other electrode. This tends to confine the discharge to the interaction space between the electrodes since any charged particles of the discharge will be quickly brought to ground potential upon making contact with the shield.
It is important to control the residence time the gases are within the interaction space between the two electrodes during processing of a workpiece. Historically, fast gas flow and low residence times have tended to give rise to discharges outside the space enclosed by the confining members (elements). This reduces the controllability of the operation and also may result in an undesirable formation of various deposits on the walls of the etching chamber.
For modern device geometries and dimensions, it is desirable to have plasma etching apparatus in which the discharge is maintained within the interaction space and in which the gases used can be relatively quickly passed through the apparatus so as to enhance control of etch parameters such as profile control and etch selectivity. This reduces the time for processing and thus reduces the over all cost of the integrated circuits being produced on the semiconductor wafers. In addition, it limits undesirable deposits from forming on walls of the etching chamber.